The invention concerns a process for producing blow molding parts having a decorative coating provided in a visible region of the blow molding parts. The decorative coating material is placed into the cavity of a blow mold tool, which is formed by two mold halves. The decorative coating material is then molded onto the blow molding part under pressure and is bonded to its surface during the blow molding. The invention also concerns a blow mold tool for carrying out the process.
In known blow molding processes, a decorative coating of textile material, leather, film or other sheet-like structures and, subsequently, a freshly extruded polymer parison or tube are introduced into the initially opened mold tool. After closing of the blow mold tool and the associated closing of the end openings of the polymer parison, air is blown into the latter. As a result, the walls of the parison, and consequently also the inserted decorative material, are pressed under high pressure and at high temperature against the inner contours of the cavity formed by the two mold tool halves. The high pressure and temperature loading of the decorative material leads not only to changes in color but also to an impairment of the surface structure and, in particular in the case of foam-backed decorative materials, to a compressing of the decorative coating, so that the elastic effect of the foam underlay is lost. If there is a premature contact between the very hot polymer parison and the decorative material, a complete, distortion-free coating cannot be ensured.
It is accordingly an object of the invention to provide a process for producing blow molding parts provided with a decorative coating that overcomes the above-mentioned disadvantages of the heretofore-known processes of this general type and which meets high quality requirements with regard to the optical and haptic formation of the blow molding parts in the region of the decorative coating. A further object of the invention is to provide a blow mold tool suitable for carrying out the process according to the invention.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for producing a blow molding part with a decorative coating in a visible region of the blow molding part, the method includes the steps of initially, as part of a multi-stage process, forming a blow molding part in an uncoated state in a blow mold tool cavity under pressure; one of placing and molding a decorative coating material against a mold tool contour in a decorative coating cavity formed substantially identical to the blow mold tool cavity; holding the decorative coating material against the mold tool contour; and subsequently molding and bonding the decorative coating material against an outer contour of the blow molding part in a mold cavity formed by mold contours of the blow mold tool cavity and the decorative coating cavity.
In other words, the object of the invention is achieved with a multi-stage process by initially forming an uncoated blow molding part in a blow mold tool cavity under pressure and placing, molding or shaping the decorative coating material against a mold tool contour in a substantially identically formed decorative coating cavity and subsequently molding it against the outer contour of the blow molding part and bonding it with the latter under reduced blowing pressure in a further mold tool cavity, formed by the mold tool contours of the blow mold tool cavity and the decorative coating cavity.
With the objects of the invention in view there is also provided, a blow mold tool, including a first mold tool contour and a second mold tool contour, the first and second mold tool contours forming a blow mold tool cavity for molding a blow molding part in an uncoated state; and a third mold tool contour and a fourth mold tool contour, the third and fourth mold tool contours forming a decorative coating cavity for molding a decorative coating material of a given thickness against the fourth mold tool contour, the fourth mold tool contour having a molding region for the decorative coating material and being widened in the molding region by the given thickness in comparison with the blow mold tool cavity.
In other words, the blow mold tool according to the invention for carrying out the process is characterized by a blow mold cavity formed by two first mold tool contours for the molding of an uncoated blow molding part and by a decorative coating cavity, formed by two second mold tool contours, for molding or placing the decorative coating material against the mold tool contour, the decorative coating cavity being widened in the molding region of the decorative coating material, by the thickness of the decorative coating material, in comparison with the blow mold cavity.
With the process according to the invention and the correspondingly configured blow mold tool it is possible to produce coated blow molding parts whose decorative coating material is not impaired with regard to color and structure by the high pressures and temperatures prevailing in the customary blow-molding and coating process. In particular, foam-backed decorative layers retain their original elastic and consequently haptically advantageous properties. In addition, the decorative coating material is bonded over its full surface area and without distortion to the blow molding part. Consequently, coated blow molding parts which meet high quality requirements with respect to their haptic and optical formation are provided.
In accordance with another mode of the invention, the close contact with which the decorative coating material is placed against the mold tool contour in the decorative coating cavity is brought about by the effect of a vacuum on the coating material. The decorative coating material therefore adapts itself to the mold tool contour and, moreover, is held against it. Blistering on the finished part is avoided.
In accordance with yet another mode of the invention, the decorative coating material is preferably heated up in advance or inside the decorative coating cavity by heating elements provided in the latter, in order to ensure a high degree of flexibility and consequently close contact with the mold contour.
In accordance with another mode of the invention, the decorative coating material is preformed and introduced into the decorative coating cavity.
In accordance with a further mode of the invention, the bonding of the decorative coating material with the blow molding part may take place directly with the still warm surface of the latter or on a co-extruded layer in the case of a polymer parison produced by co-extrusion and/or with the use of a coupling agent.
In accordance with a further mode of the invention, a surface of the blow molding part suitable for bonding with the decorative coating material is created by another surface layer, formed by co-extrusion of the original parison.
In accordance with yet a further mode of the invention, a foam material suitable for bonding with the decorative coating material is applied in advance to the rear side of the decorative material and this foam layer is used for the bonding of the decorative layer and the substrate part.
In accordance with another mode of the invention, an air gap is left in the decorative coating cavity between the decorative coating material and the blow molding part and a foam material and/or synthetic material is introduced into the air gap for bonding purposes.
In accordance with a further mode of the invention, initially the decorative coating material is produced in the decorative coating cavity by a separate injection-molding and/or foaming operation and is subsequently bonded with the blow molding part.
In accordance with another feature of the invention, the blow mold tool is of a three-part configuration and includes two side parts and a middle part provided between the latter, these parts are respectively movable or pivotable. The blow mold tool cavity is formed between the middle part and one side part by corresponding mold tool contours. The decorative coating cavity is produced in a similar way between the other side part and the other side of the middle part. The suction action on the decorative coating material originates from a vacuum chamber accommodated in the relevant side part.
In accordance with another feature of the invention, the middle part can be moved or pivoted in a direction perpendicular to the direction of movement of the side parts.
In accordance with yet another feature of the invention, the decorative coating cavity is integrated in a vacuum chamber.
In accordance with a further feature of the invention, suction openings connected to the vacuum chamber are provided in the side part receiving the decorative coating material, in the region of the mold tool contour, in order to extract all the air from the space and to avoid the formation of air bubbles on the finished part.
In accordance with another feature of the invention, heating elements for heating up the decorative coating material are provided in the decorative coating cavity.
In accordance with yet another feature of the invention, the first mold tool contour has in the blow mold tool cavity holding devices for holding the blow molding part after its release from the mold contour of the middle part.
In accordance with another feature of the invention, the holding devices for holding the blow molding part are formed by undercuts or retaining cores.
In accordance with another feature of the invention, at least one slide, directed into the blow mold tool cavity, is provided on the middle part for producing undercuts, the corresponding side part being provided in a pivotable manner and the mold tool regions being correspondingly beveled in the separation or parting.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a process for producing blow molding parts with a decorative coating and a corresponding blow mold tool for producing such blow molding parts, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.